Preheat your oven to 180°c (160°c for fan assisted oven or Gas Mark ) and lightly grease a couple of baking sheets with a little butter.
In a large bowl, cream the butter, peanut butter and sugar together until light and fluff.
Add the egg and vanilla and mix until combined.
Sift in the flour and mix to make a dough.
Roll the dough into balls (about 1 tbsp of dough per ball) and place onto your pre-greased baking sheets. Press each ball lightly with the back of a fork to create a cross pattern.
Bake in your pre-heated oven for 15-20 minutes until golden.
Once cool enough to touch, transfer to a wire rack to cool completely.